1. Field of the Invention
The invention relates to a power source unit which has a secondary battery and an AC adapter therein and is suitable for use as a power source of, for example, a portable personal computer.
2. Description of the Related Art
In recent years, various portable personal computers of a light weight, a small size, and a high operability have been proposed in association with development of a liquid crystal technology. For example, as for the size, the portable personal computers of the A4 or B5 size have generally been widespread. Many compact digital cameras, camera integrated type VTRs, and the like have been put into practical use in association with the development of the electronic image technique. Those camera apparatuses have an excellent using efficiency in terms of easiness of image processes, easy operation of a reproducing process, and the like, so that they are generally and preferably used in association with the spread of personal computers. Further, cellular phones have also been widespread to each home and become common owing to the development of the communicating technique and the widespread of communication services. Portable information terminals called PDA (Personal Digital Assistants) have also been put into practical use. Such a PDA is a multipurpose terminal having a telephone function using a digital radio telephone system called PHS (Personal Handy Phone System), a communicating function for communicating with a personal computer, a facsimile apparatus, or the like, and a function called an electronic notebook and has about a size of a palm.
In those portable electronic apparatuses, ordinarily, a secondary battery which is reusable by charging is used for an economic reason or the like, and when they are carried, a battery unit comprising a plurality of secondary batteries which are serially connected is used as a DC power source, and an internal electronic circuit is driven by an output of such a battery.
Upon charging, in a portable personal computer or a PDA, since a charging circuit of the secondary battery is provided integratedly with the main body side, it is sufficient to merely prepare an AC adapter. That is, in case of using such a personal computer or a PDA indoors or the like, that is, at a place where a commercially available power source or the like has been arranged, an AC power source of 100V is converted into a predetermined DC voltage by the AC adapter, the internal electronic circuit is driven by an output of the DC voltage, the secondary battery is disconnected from a power line, and the charging circuit is made operative, thereby charging the secondary battery.
On the other hand, in a cellular phone, a digital camera, or the like in which the charging circuit of the secondary battery is not provided integratedly with the main body side but a DC/DC converter for regulating an output voltage of the secondary battery is installed, the relation between the secondary battery and the main body side is unclear and dedicated charging devices are necessary. Each of those dedicated charging devices is constructed by an AC adapter, a charging circuit, and the like, the main body or a battery unit is installed to the dedicated charging device when it is not carried, and the secondary battery is charged.
In the case where the charging and discharging are simultaneously performed to/from the secondary battery, however, not only the output voltage is not set to a predetermined value but also the secondary battery is accompanied with a heat generation or a vibration, and an inconvenience occurs. Therefore, a power source unit having a higher safety in which the charging and discharging to/from the secondary battery can be strictly managed is demanded.
It is, therefore, an object of the invention to provide a power source unit having a higher safety in which the charging and discharging to/from the secondary battery can be strictly managed.
To solve the above problems, according to the invention of claim 1, there is provided a power source unit which is arranged between a commercially available power source and an electronic apparatus having a secondary battery therein and supplies an output voltage to the electronic apparatus, comprising: voltage converting means for converting a voltage of the commercially available power source into a predetermined regulated DC voltage which is necessary for the electronic apparatus; a battery unit constructed by a plurality of secondary batteries; first switching means which is inserted between the voltage converting means and the battery unit; second switching means which is inserted between the voltage converting means and a power output terminal; and control means for turning off the second switching means when the first switching means is ON and turning off the first switching means when the second switching means is ON.
According to the invention, the voltage converting means, battery unit, first and second switching means, and control means are provided. For example, when the power source unit is set to a supplying mode, the voltage converting means is made operative, the second switching means is turned on, and the output voltage formed by the voltage converting means is supplied to the load side. In this state, the first switching means is controlled by a stop output from the control means, so that it is not turned on at all. When the power source unit is set to a charging mode, the voltage converting means is made operative, the first switching means is turned on, and the output voltage formed by the voltage converting means is supplied to the battery unit. In this state, the second switching means is controlled by the stop output from the control means, so that it is not turned on at all. In any setting mode, therefore, the first and second switching means are not simultaneously turned on and the safety is more raised.